In a wireless mesh network, each node communicates directly only with neighbouring nodes, which in turn relay transmissions to more distant nodes. Such networks find application in a variety of different fields, differing based on the type of digital devices found at each node. For example, such networks may be used for controlling lights in an office building, with each light device being connected to a node of the network and communicating wirelessly with neighbouring nodes; or for communicating between a network of water sensor devices at a water purification plant, or for communicating between members of a wireless network of computer systems. The low power requirements of wireless communications to a neighbouring node, for example when each node is only a few meters distant from neighbouring nodes, mean that mesh networks can be made using relatively inexpensive transceivers.
U.S. Pat. No. 6,028,857 of Poor identifies several types of prior art mesh networks. In a first type of mesh network, the Link State Routing system, each node maintains a routing table that specifies an optimal path toward each network destination. An originating node sends a message by broadcast to all neighbouring nodes, but only the specified recipient node along the optimal path relays the message, as determined by each node consulting its routing table; until the message reaches its destination. In a second type of mesh network, the Source Path Routing system, the originating node sends a message containing the entire route of the message; each node then passes the message along the specified route until the destination node is reached.
Both of these types of wireless mesh network require that each node keep a record of its neighbouring nodes, and broadcasts changes in its list of neighbouring nodes. Among other things, the use of these messages consumes bandwidth and power, and risks breakdown due to errors in transmitting the updated neighbour lists.
In the technique of U.S. Pat. No. 6,028,857 of Poor, each member node of the mesh network maintains a cost table that indicates the costs of transmission to other nodes in the network. These cost tables are dynamically generated, based on the number of “hops” required to transmit messages from an originating node to a destination node. New nodes may therefore be added to the network quite flexibly, simply by having the node transmit a message; and node locations may be changed by simply changing the nodes' locations, and beginning to transmit messages. There is no requirement for each node to maintain a routing list of network neighbours, or to transmit updates to the list of neighbouring nodes.
However, there is an ongoing need for wireless mesh networks with low power requirements, which can quickly determine the lowest cost transmission route from an originating node to a destination node.